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Gene Regulation
GENE REGULATION
in
Eukaryotic Cells
Every cell in a multi-cellular eukaryote has a copy of all genes.
However, different genes are actively expressed in
different cells
Chapter 15
Gene Regulation
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Gene Regulation
Eukaryotic Regulation
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A variety of mechanisms
Five primary levels of control:
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Nuclear levels
Chromatin Packing
 Transcriptional Control
 Posttranscriptional Control
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Cytoplasmic levels
Translational Control
 Posttranslational Control
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Gene Regulation
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Regulation of Gene Expression:
Levels of Control in Eukaryotes
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Chromatin Structure
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Eukaryotic DNA associated with histone
proteins
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Together make up chromatin
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As seen in the interphase nucleus
Nucleosomes:
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Gene Regulation
DNA wound around balls of eight molecules of
histone proteins
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Looks like “beads on a string”
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Each bead a nucleosome
The levels of chromatin packing determined
by degree of nucleosome coiling
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Gene Regulation
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Levels of Chromatin Structure
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Gene Regulation
Chromatin Packing
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Euchromatin
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Loosely coiled DNA
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Transcriptionally active
Heterochromatin
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Tightly packed DNA
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Transcriptionally inactive
Barr Bodies
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Females have two X chromosomes, but only
one is active
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Other is tightly packed along its entire length
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Inactive X chromosome
is Barr body
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X-Inactivation in Mammalian Females
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Non-Coding DNA
• 97% of human DNA is non-coding
• Repetitive DNA not in genes
• Tandemly repetitive DNA
short sequences repeated in series
DNA Methylation
The attachment of methyl
groups to DNA bases
Inactivates the genes
Demethylating certain
inactive genes turns them
on.
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Histone Acetylation
Acetyl groups attaching to histones
Acetylated histones grip DNA less
tightly allowing for transcription to
occur more easily
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Gene Regulation
Transcriptional Control
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Transcription controlled by proteins
called transcription factors
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Bind to enhancer DNA
Regions of DNA where factors that
regulate transcription can also bind
Always present in cell, but most likely
have to be activated before they will
bind to DNA
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Initiation of Transcription
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Gene Regulation
Posttranscriptional Control
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Posttranscriptional control operates on
primary mRNA transcript
Given a specific primary transcript:
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Excision of introns can vary
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Splicing of exons can vary
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May also control speed of mRNA transport
from nucleus to cytoplasm
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Determines the type of mature transcript that
leaves the nucleus
Will affect the number of transcripts arriving at
rough ER
And therefore the amount of gene product
realized per unit
time
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Processing of mRNA Transcripts
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Gene Regulation
Translational Control
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Translational Control - Determines
degree to which mRNA is translated
into a protein product
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Presence of 5′ cap
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Length of poly-A tail on 3′ end
Posttranslational Control - Affects
the activity of a protein product
Chapter 15
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Activation
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Degradation rate
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Gene Regulation
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Chapter 15
http://www.sciencemag.org/cgi/con
tent/full/319/5871/1781b
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